The basic problem of dyeing

1. Dyeing process

The dyeing process can be roughly divided into three stages:

A. Absorbing

Adsorption is the process in which the dye attaches to the surface of the fiber; the dye is adsorbed by the fiber in the solution due to the intermolecular force and the electrostatic attraction between ions.

B. Diffusing and penetreating (diffusing and penetreating)  

After adsorption, the dye needs to enter the fiber and keep it inside; under certain conditions, the adsorbed dye diffuses and penetrates from the surface of the fiber to the inside of the fiber, enters the amorphous area of the fiber, and reaches the dye solution, the surface of the fiber and the dye inside the fiber. The concentration reaches equilibrium.

C. Fixing (fixing)

This is a key process for the color fastness; the dye entering the amorphous region of the fiber is connected to the fiber macromolecule by chemical force (ionic bond or covalent bond) intermolecular attraction (van der Waals force) and hydrogen bond. The binding fastness.

In actual dyeing, the above three stages cannot be clearly distinguished. Different dyes, different fibers, different dyeing processes, and the dyeing process are also different.

2. The affinity and directness of the dye 

A certain dye can automatically dye a certain fiber in the solution, and we say that the dye has affinity or directness for this fiber. The faster the dyeing speed and the higher the dyeing percentage, the greater the affinity or directness of the dye. Both concepts are used to explain the dye uptake ability, but affinity is a strict thermodynamic concept with a certain thermodynamic value; directness has no exact quantitative concept, but can only explain the dye uptake ability in general.

The dyeing speed is fast when the dye affinity is high, and there is no need for excessive dyeing promotion, but the dyeing is possible, the affinity is low, it needs to promote the dyeing, and the dye may be wasted.

3. Dye uptake rate

When the dyeing reaches equilibrium, the ratio of the amount of dye dyed to the fiber to the original dye amount in the dye liquor is usually expressed as a percentage, which is called the dye uptake rate or equilibrium dye uptake percentage.

4. Dyeing rate

The dye uptake rate refers to the speed at which the dye is absorbed and dyed by the fiber. It is often expressed as the "half dyeing time", that is, the time required for the dye to reach half of the dyeing equilibrium dye uptake under specified conditions. Too fast dyeing will easily cause uneven dyeing, and too slow dyeing will prolong dyeing time.

5. Dye migration (level dyeing)

Dye migration refers to the ability of the dye that has been absorbed by the fiber to desorb from the fiber, re-enter the dye solution and then dye another part of the fiber. The dye with good migration ability can continuously desorb from the high dye concentration and dye it at the low concentration until the concentration difference disappears on the whole fabric, which is beneficial to level dyeing.